1. Field of the Invention
The present invention relates to an ink-jet printer, and more in particular, the present invention relates to improvements in imparting vibration to the ink inside the ink nozzle of an ink-jet printer.
2. Description of the Prior Art
An ink-jet printer is a non-impact type printer and it includes an ink nozzle from which ink droplets are discharged under electrostatic acceleration to be impinged, after suitable deflection, upon a recording medium in a dot-matrix format to form characters thereon. In such an ink-jet printer, it has been well known to pressurize and impart vibration to the ink inside the nozzle in order to product desired ink droplets. In prior art ink-jet printers, use was made of an electrostrictive vibrator to impart vibration to the ink inside the nozzle. There were two conventional approaches in driving such as electrostrictive vibrator. One approach was the resonant method in which the frequency of the driving electrical signal was made equal to the resonant frequency of an electrostrictive vibrator; the other approach was the non-resonant method in which the two frequencies were set differently so as not to establish a particular relationship therebetween.
It is true that the conventional resonant method is high in vibrating efficiency, but it is extremely unstable since the resulting output drastically changes due to slight changes in external conditions or the like. The non-resonant method is quite opposite to the resonant method and unstability such as described above does not exist. However, the vibrating efficiency of the non-resonant method tends to be low and therefore it is required to provide a high power vibrator. Another approach has been proposed to apply a driving electrical signal having a modified waveform to the electrostrictive vibrator in order to prevent production of unwanted ink satellites between ink droplets to be used for forming characters on a recording medium. Although this last approach is effective in preventing production of unwanted ink satellites, an optimum waveform of the driving electrical signal must be determined in consideration of structual elements such as the electrostrictive vibrator and the liquid chamber of the ink nozzle. Determination of such an optimum waveform is quite difficult. Besides, it requires to provide an oscillating circuit of complicated structure, which, in turn, pushes up the manufacturing cost.